The present invention relates to technology for jetting ink droplets from a plurality of nozzles so as to print dots on the surface of a printing medium and thereby print images, and more particularly to printing technology utilizing dot dropout inspection that detects whether ink droplets are jetted from each nozzle.
An inkjet printer prints images by jetting ink droplets from a plurality of nozzles. A print head of an inkjet printer is provided with a large number of nozzles. However, it sometimes happens that, because of an increase in ink viscosity, the ingression of air, or some other cause, one or more nozzles become clogged and unable to jet ink droplets. The clogging of nozzles, by resulting in the dropout of dots from the image to be printed, is a cause of degradation in image quality.
Conventionally, inspection for clogging would be carried out by the printing of a test pattern on printing paper prior to a printing job and by visual inspection of that test pattern by the user. In this Description, the term xe2x80x9ca printing jobxe2x80x9d refers to the entirety of printing operations that are carried out in accordance with a single instruction by a user.
Conventionally, because inspection would be carried out only before a printing job was started, there occurred the problem of failure to achieve the desired image quality because of dot dropout occurring during printing operations.
An objective of the present invention is to provide technology capable of mitigating degradation of image quality when dot dropout occurs during printing operations.
In order to at least partly resolve the problem, the present invention carries out bidirectional normal printing operations wherein forward feeding sub-scan and back feeding sub-scan are alternately carried out between the outward pass and return pass of main scanning. Furthermore, after each round trip pass of printing operations, an inspection for the jetting of ink droplets from each nozzle is carried out to determine whether each nozzle is an operational nozzle, which is capable of jetting ink droplets, or a non-operational nozzle, which is incapable of jetting ink droplets. When a non-operational nozzle is present, a round-trip pass of supplementary operations, wherein dots to have been printed by a non-operational nozzle are printed with another, operational nozzle, are carried out.
By thus supplementing dots using another, operational nozzle when a non-operational nozzle is detected, the degradation in image quality that would otherwise result from dot dropout occurring during printing operations can be mitigated. In particular, because sub-scanning that alternates between forward feeding and back feeding is carried out in normal printing operations, sub-scanning feeding error that may occur in supplementary operations when back feeding is necessary in supplementary operations is roughly equivalent to that occurring in the normal printing operations. As a result, image quality degradation arising from large sub-scanning feeding error can be mitigated.
In addition, it is preferable for the forward feeding sub-scan is carried out by a first feed amount before the outward pass of main scanning in the normal printing operations, and that the back feeding sub-scan is carried out by a second feed amount that is less than the first feed amount before the return pass of main scanning in the normal printing operations. In so doing, because the print head will have moved by the back feeding prior to the return pass of main scanning that, in normal printing operations, is carried out immediately prior to supplementary operations, the sub-scanning feed amount necessary to carry out supplementary operations can be relatively short. Therefore, feeding error in supplementary operations is also kept low.
In addition, it is preferable that forward feeding sub-scan is carried out before an outward pass of main scanning in the supplementary operations, that back feeding sub-scan is carried out before a return pass of main scanning in the supplementary operations; and that forward feeding sub-scan is carried out after a return pass of main scanning in the supplementary operations but before an outward pass of main scanning in the normal printing operations. In so doing, because forward feeding and back feeding are also carried out alternately in supplementary operations, sub-scanning feeding error in supplementary operations can be kept roughly equivalent to that of normal printing operations.
Furthermore, it is preferable for supplementary operations to be operations wherein only dots located on a main scanning line that was to have been printed by a non-operational nozzle are printed using another, operational nozzle. In so doing, it is possible to prevent the degradation in image quality that would result from overprinting of correctly-printed dots located on other main scanning lines.
In addition, when a non-operational nozzle is detected, cleaning of the non-operational nozzle may be carried out before the supplementary operations, and, in the event that a predetermined number of cleanings fails to restore operation of the non-operational nozzle, a first supplementary operation wherein dots to have been printed by the non-operational nozzle are printed by another, operational nozzle may be carried out. In so doing, dot dropout can be resolved even if a predetermined number of cleanings fail to restore nozzle operation.
Moreover, when a non-operational nozzle is restored within a predetermined number of cleanings, a second supplementary operation wherein the restored, now operational nozzle is used to print dots to have been printed by that the non-operational nozzle may be carried out. In so doing, dots that were initially omitted by a non-operational nozzle can be printed by the nozzle that was originally to have printed the dots, thus simplifying dot supplementation.
Furthermore, the present invention can be realized in various configurations including printing methods; printing apparatus; computer program products that implement the printing methods or the functions of printing apparatus; other computer programs; and data signals embodied in a carrier wave including the computer programs.